How to Cope Joints

The secret for a glove-tight fit for trim corners is a coped joint. With this technique you can even make complex crown moldings fit without leaving gaps. Because inside corners are rarely square, simply butting two mitered pieces into the corner almost always looks lousy. The only foolproof method for great-looking inside corners is cutting a coped joint. This age-old carpenter's trick involves cutting the profile on the end of one molding and fitting it against another like pieces of a puzzle. The resulting joint is easy to file and sand for a perfect fit, even on out-of-square corners. In this article we'll walk you through the key techniques, step by step, and you'll be cutting perfect copes in no time.

Start by purchasing a coping saw

Coping saw

The coping saw's thin blade allows you to saw curves and cut into tight corners.

Copes are sawed with—you guessed it—a coping saw. You don't need to spend a lot of money on one, however. The basic version available at hardware stores, home centers and lumberyards works great. Pick up an assortment of blades. Use fine-tooth blades for thin material and intricate cuts. A blade with 20-teeth per inch works well for most copes. Some carpenters prefer to cut copes with a jigsaw. If you own a jigsaw, install a fine-tooth blade and give it a try.

A coping saw is designed to cut on the pull stroke (with the blade's teeth facing the handle). But many carpenters, myself included, prefer to mount the blade with the teeth facing away from the handle so the saw cuts on the push stroke. Try it both ways and decide for yourself which method you prefer.

Rough cut the molding profile

Photo 1: Reveal the profile

Bevel the end of the molding to be coped at a 45-degree angle to reveal the profile.

Photo 2: Guide the blade

Guide the blade with your thumbnail to start the cut accurately. If your molding has a little flat spot on top like ours, start the cut with the blade of the coping saw held perpendicular to the molding to make a square starting cut.

Photo 3: Cut just outside the line

Angle the coping saw about 30 degrees to remove more wood from the back of the molding than the front. Then slowly and carefully saw along the profile. Concentrate on staying just outside the line. You can always sand or file away extra material.

Photo 4: Cut at different angles

Restart the cut to saw around sharp curves or to cut out notches. Complex shapes like this may require three or four approaches at different angles.

The first step in coping is to establish the cutting line. Cutting a 45-degree bevel (Photo 1) is the easiest method if the two moldings you're joining have the same profile. The molding shown has a complex profile, making for a challenging coping job. Most of the moldings you'll encounter will be considerably easier. Crown and cove moldings that rest at an angle against the wall and ceiling require a slightly different beveling technique to reveal the profile for coping. Photo 7 shows you how to position a crown molding in your miter box to cut this bevel.

Photo 2 shows you how to start the cope. The technique varies slightly depending on the profile of the molding. Moldings like ours with flat spots on the top require a square starting cut. If you start angling the cut too soon, you'll see a little triangular gap on the top of the moldings when you join them. Cut a practice cope on a scrap to confirm your starting angle.

Clamp the molding to a sawhorse or hold it in place with your knee while you saw. Don't force the blade. If the blade starts to leave the cutting line, back up a little and restart the cut. On steep curves, the frame of the saw may hit the molding. If this happens, back the saw out of the cut and saw in from the opposite direction.

You may be able to complete some simple copes with one long cut, but in most cases you'll have to approach them from two or three different angles to finish the job (Photos 3 and 4).

Test fit and file for a perfect joint

Photo 5: Mark trouble spots

Check the fit of the coped joint. Use a sharp pencil to mark spots that have to be sanded or filed.

Photo 6: File or sand trouble spots

File or sand off high spots. Use rolled-up sandpaper or a rattail file to fine-tune curved sections. Continue checking the fit, then filing or sanding until the joint fits tight.

After a few minutes of sawing, the cut will be complete; now it's time to test-fit the cope on a matching piece of trim. Some copes fit perfectly on the first try. Others require several more minutes of filing and sanding before you get a good fit (Photo 6). If the joint is close to fitting, you'll only need to touch up the high spots with 100-grit sandpaper. Use files to remove larger amounts of material.

Special techniques for crown molding

Photo 7: Cutting the bevel in crown molding

Position your crown molding upside down in the miter box at the angle it will rest on the wall (flat spots tight to the bed and fence). Screw or clamp a stop to the extension table to support the crown molding at the correct angle.

Photo 8: Recut for a tight fit

Cope crowns at a sharper angle. Recut areas that are hitting in the back. It's common to have to remove large amounts of material in some areas to get a tight fit.

Photo 9: Perfect crown molding

Measure and cut the end of the first crown molding square. Butt it into the corner. Don't nail within 16 in. of the corner. Cope the second piece of crown molding and file and sand it for a perfect fit.

Photo 7 shows you how to position the crown molding upside down in your miter box for cutting the bevel. Attach a wood stop to the extension table to hold the molding at the correct angle. Sawing copes on crowns, especially large ones, requires more effort because the angle of the cut has to be about 50 degrees—much steeper than for a baseboard cope. Even experienced carpenters cut this angle too shallow once in a while. Usually one or two areas will hit in the back and you'll have to remove more material (Photo 8).

Switch to a blade with fewer teeth for cutting thick materials like crown moldings. Then expect to spend 10 or 15 minutes on each joint to get a perfect fit. Before you tackle crown molding copes, practice on smaller moldings like base shoe or simple baseboards to gain confidence. Once you've mastered coping you'll never miter an inside corner again.